/Engine/Plugins/Importers/USDImporter/Source/UnrealUSDWrapper/Public/UsdWrappers/SdfLayer.h
In the USD API, pxr::SdfPayload and pxr::SdfReference are very similar except that the latter includes support for a custom data dictionary. The UE wrapping of SdfReference does not currently include support for that custom data, leaving theFSdfReferencewrapper identical to theFSdfPayloadwrapper. We keep them as distinct types though to better mimic the USD API and in case support for custom data dictionaries on references is added to theFSdfReferencewrapper in the future.
struct FSdfReference
FString
AssetPath
FSdfLayerOffset
LayerOffset
FSdfPath
PrimPath